comeback days

The few days or week after a break up where you make sure you look your best in front of your ex to let them know what they're missing.

comeback ex moving on

Hannah: Stacy why have you been looking so good these past few days?!

Stacy: ohh you know it's the comeback days !

Comeback day

The day you come back to a game (usually gacha) to lots of rewards for being inactive

Person 1: Bro why haven’t you been online on Super Cool Game for 3 weeks?
Person 2: I’m waiting for my comeback day.